Self-healing electrical condenser

ABSTRACT

A first and at least two second electrodes are provided, with the latter flanking the former. First dielectric separating means is provided between the first electrodes and one of the second electrodes and has n paper strips and m synthetic plastic strips with n being a whole number excluding zero and one, and m being a whole number including zero and one, and with n being greater than m. Second dielectric separating means is provided between the first electrode and the other of the second electrodes and comprises N plastic strips and M paper strips with N being a whole number including one, M being a whole number including zero and N being greater than M. The electrodes are each applied to one side of two paper strips and the latter have uncovered sides facing one another, with the first and second dielectric separating means being electrically connected in parallel with each other.

United States Patent Maylandt et al.

[54] SELF-HEALING ELECTRICAL CONDENSER [72] Inventors: Helmut Maylandt,Plochingen; Herbert Forster, Grunbach; Josef Juhasz, Stuttgart, all ofGermany [73] Assignee: Robert Bosch Gmbll, Stuttgart, Germany [22]Filed: Dec. 14, 1971 [21] Appl. No.: 207,884

52 u.s.c| ..3l7/258,3l7/260 51 lnt.Cl. ..H01g3/2l5 5s FieldofSearch..3l7/258,260

[5 6] References Cited UNITED STATES PATENTS 3,596,l52 7/l97l Allison..3l7/258 Primary Examiner-E. A. Goldberg Attorney-Michael S. Striker 1Oct. 17, 1972 [5 7] ABSTRACT A first and at least two second electrodesare provided, with the latter flanking the former. First dielectricseparating means is provided between the first electrodes and one of thesecond electrodes and has n paper strips and m synthetic plastic stripswith n being a whole number excluding zero and one, and m being a wholenumber including zero and one, and with n being greater than m. Seconddielectric separating means is provided between the first electrode andthe other of the second electrodes and comprises N plastic strips and Mpaper strips with N being a whole number including one, M being a wholenumber including zero and N being greater than M. The electrodes areeach applied to one side of two paper strips and the latter haveuncovered sides facing one another, with the first and second dielectricseparating means being electrically connected in parallel with eachother.

8 Claims, 3 Drawing Figures sexwww ya Q///////// 'X f/ f/ff PATENIEDHBT1 I912 3,699,410

Fig-

Fig-2 1 SELF-HEALING ELECTRICAL CONDENSER BACKGROUND OF THE INVENTIONThe present invention relates generally to electrical condensers andmore particularly to self-healing electrical condensers.

Self-healing condensers are already well known in the art and are notbelieved to require any detailed explanatory discussions. Among these itis known to provide a-construction having a paper strip which carries ametallic coating as an electrode, with a synthetic plastic layer beingjuxtaposed with the paper strip at the side remote from the electrodeand with another electrode being applied to the exposed side of thesynthetic plastic strip. Between two electrodes of opposite sign thereare thus interposed the paper strip and the plastic strip.

Another known construction utilizes two electrodes of opposite signbetween which there are dielectric of polyethylene-terephthalate, or ofa laminate of such material with paper. ln addition, there is a furtherundefined laminate of paper and polyethylene-terephthalate provided, andthe construction may vary depending on whether the electrodes areapplied to the exposed surfaces of papers or polyethylene-terephthalatestrips.

Other constructions are also known but they share with theaforementioned ones the characteristic that the sequence and arrangementof paper and plastic strips is selected irrespective of the stronglydifferent dielectric characteristics of these materials. Evidently, thisis not satisfactory and further improvements are therefore desirable andhave been sought in the art.

SUMMARY OF THE INVENTION lt is, accordingly, a general object of theinvention to provide such improvements.

More particularly it is an object of the present invention to provide animproved self-healing electrical condenser which has incorporated theaforementioned desirable improvements.

ln pursuance of these and other objects which will become apparenthereafter, one feature of the invention resides in a self-healingelectrical condenser which, briefly stated, comprises at least one firstelectrode, at least two second electrodes flanking the first electrode,and first and second dielectric separating means. According to theinvention the first separating means is between the first electrode andone of the second electrodes and comprises n paper strips and msynthetic plastic strips wherein n is a whole number excluding zero andone, and m is a whole number including zero and one, with n beinggreater than m. Furthermore, the second dielectric separating means islocated between the first electrode and the other of the secondelectrodes and comprises N plastic strips and M paper strips wherein Nis a whole number including one, M is a whole number including zero,with N M, said electrodes being each applied to one side of two of saidpaper strips and the latter having uncovered sides which face oneanother, and said first and second dielectric separating means beingelectrically connected in parallel with each other.

An electrical condenser constructed in accordance with the presentinvention provides for a fuller and more effective utilization of theadvantages to be obtained. from a composite use of paper strips andsynthetic plastic strips as the dielectric of the condenser. In such aconstruction the number of paper strips between the electrodes is alwaysgreater at one side than the number of synthetic plastic strips, whereasat the other side the number of synthetic plastic strips is alwaysgreater than the number of paper strips, meaning that at the one sidethere is predominantly paper and that at the other side there ispredominantly synthetic plastic material. The advantage obtained in thismanner resides in the fact that the novel self-healing electricalcondenser has the electrodes provided exclusively on paper strips, withno electrodes being provided on the synthetic plastic strips and in thatthe exposed sides of the electrodes are under all circumstancescontacted by the plastic strips.

In this connection it is important to take into consideration that it isconsiderably less expensive to deposit the electrodes-as by vapordeposition-on paper strips than on synthetic plastic strips. The vapordeposition of the metallic material of the electrodes on the paperstrips can be carried out more rapidly than would be possible onsynthetic plastic, the metallic material will adhere better. There isfurther a lesser incidence of rejects. In fact, the deposition ofmetallic material (to form electrodes) on synthetic plastic strips isconsiderably more difficult than on paper strips and in some instancescannot even be carried out to the necessary thickness required for theelectrodes.

A further advantage of the construction according to the presentinvention is inherent in the contact of the plastic strips to themetal-coated paper strips, because the gap width between the strips isvery small so that after self healing breakdowns a high potential can bereached before the danger of corona discharge occurs.

It should be recalled here that the gap widths are determined by theroughness of the surfaces which contact one another. When paper stripssurfaces contact one another the gap width is equal to twice thesocalled rough depth of the contacting surfaces, with the term roughdepth referring to the distance between the highest and lowest points ofthe paper strip surface. On the other hand, the gap width betweencontacting paper and synthetic plastic surfaces (in the condenseraccording to the present invention) is smaller than the single roughdepth of the paper surface because the synthetic plastic material has avery smooth surface and additionally has a tendency to swell under theinfluence of impregnating media so that it at least partially fills anydepressions in the surface of the paper strip which it contacts.

The invention also provides for optimum utilization of paper andsynthetic plastic material in accordance with their voltage resistanceand/or provides for optimum permissible operating field strength bycorrect choice of the strip thicknesses. If, for instance, in a specificapplication one side of a condenser is composed of two metallized paperstrips having a thickness of 12 microns, with between them apolycarbonate strip having a thickness of 15 microns, and if the otherside of the condenser is composed of two polycarbonate strips having athickness of 8 microns and between them a paper strip having a thicknessof also eight microns, then a condenser or capacitor so constructed andsubsequently impregnated with mineral oil will have in its rolled-updielectric components a specific volume of 28 cm luF. Of course, thisexemplary condenser according to the present invention is constructedasymmetrically with respect to its dielectrics, as are all onesaccording to the present invention. If, however, the dielectric werearranged in accordance with the prior art as a symmetric mixeddielectric, meaning that at each side of the electrodes there wereprovided two paper strips having a thickness of 12 microns andintermediate them a synthetic plastic strip having a thickness of 15microns and for instance consisting of polycarbonate, then acorresponding volume of 41 cm luF would be obtained..lt is readilyevident therefore that the volume of the condenser constructed accordingto the present invention is approximately 32 percent smaller than thatof a similar condenser constructed in accordance with the prior art. Inaddition, the condenser according to the present invention has lowerdielectric losses because on the side. in which the dielectric ispredominantly composed of synthetic plastic strips are smaller than thelosses at the other side.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims.

The invention itself, however, both as to its construction and itsmethod of operation, together with additional objects and advantagesthereof, will best be understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial section through arolled self-healing condenser according to one embodiment of theinvention;

FIG. 2 is a view similar to FIG. 1 but of a further embodiment of theinvention; and

FIG. 3 is a view similar to FIG. 1 but of still another embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now the drawing indetail, and firstly the embodiment illustrated in FIG. 1, it will beseen that this Figure illustrates a self-sealing condenser according tothe present invention having three dielectric strips, a syntheticplastic strip and two paper strips each of which latter carries on oneexposed side a electrode which is provided by metallic vapor depositionand whose uncoated sides contact oneanother. As pointed out earlier,this condenser thus has the electrodes provided exclusively on paperstrips.

FIG. 1 shows that there is provided one first electrode l and a secondelectrode 14 which, when the assembled strips are rolled up to theconfiguration of FIG. 1, actually constitutes with its differentportions two second electrodes 14 which flank (are located at oppositesides of) the electrode as illustrated. The electrodes 14 and 15 areprovided on one side each of two paper strips16 and 17, as by vapordeposition. The non-coated or metallized sides of the paper strips 16and 17 contact one another, a construction which is particularlyadvantageous if the condenser is to be used for higher winding potentialand to be particularly resistant.

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Located between the exposed side of theelectrode l5 and that portion ofthe electrode 14 which will face the exposed side of the electrode 15when the assembly is rolled up to the configuration of FIG. l, is astrip of synthetic plastic material, identified with reference numeral18. In this embodiment, as in the others to be discussed, it should beunderstood that various different synthetic plastics well known to thoseskilled in the artare suitable. This includes in particular low-losssynthetic plastic foils which may be made of polycarpolypropylene,polyphenylene polytetrafluoroethylene, polysulfone and other plastics.

It is quite evident that at one side of the condenser of FIG. 1, that isat one side of .the electrode 15, the number n of paper strips 16 and 17is greater than the number m of plastic strips 18, namely in theillustrated embodiment there are at this side no synthetic plasticstrips at all. On the other hand, on the other side of the electrode 15,between it and the facing portion of the electrode 14, the number N ofplastic strips 18 is greater than the number M of paper strips, namelyin the illustrated embodiment there are at the side no paper strips atall.

If the condenser according to the present invention is constructed witha synthetic plastic material having particularly high potentialresistance, then it may be advantageous to so construct the condenserthat the paper component of the dielectric is not in form of two layersor strips but is in the form of three layers. FIG. 2 shows such anembodiment in which there are provided two paper strips 21 and 22analogous to the strips 16 and 17 of FIG. 2 and each carrying at anexposed side one of the vapor-deposited electrodes 19 and 20. Locatedbetween the juxtaposed non-coated surfaces of the paper strips 21 and 22is a further non-coated paper strip 23. This assembly is then rolled upto the configuration of FIG. 2, with again a synthetic plastic strip 24being provided which is located between the exposed side of theelectrode 20 and that portion of the electrode 19 which on rolling upwill become juxtaposed with the exposed side of the electrode 20. FIG. 3shows an embodiment of a condenser which is suitable if still highervoltages are to be utilized than are permissible in the embodiments ofFIGS. 1 and 2. In this case there are provided two paper strips 27 and28 analogous to the strips 21 and 22 of FIG. 2 and each provided on anexposed side with one of the electrodes 25 and 26 which isvapor-deposited thereon. The noncoated surfaces of the paper strips 28and 27 face one another and juxtaposed with them and sandwiched betweenthem is a synthetic plastic strip 29. When this assembly is rolled up sothat again a portion of the electrode 25 will face the exposed side ofthe electrode 26, there will be located between this exposed side of theelectrode 26 and the aforementioned portion of the electrode 25 adielectric component composed of two synthetic plastic strips 30 and 31one of which is in contact with the exposed side of the electrode 26 andthe other of which is in contact with the exposed side of the portion ofthe electrode 25 which is juxtaposed with the electrode 26. Locatedbetween these plastic strips 30 and 31 and sandwiched between them is apaper strip 32.

If the novel condensers are to be used with alternating potential, theyare saturated with an auxiliary liquid dielectric, for instance mineraloil. In such an embodioxide,

ment the lowest increase of the loss factor and the highest potentialresistance before the beginning of corona discharge and breakdown isobtained when the gap for the saturating liquid (adjacent one of theelectrodes) has intermediate the electrode and the adjacent stripcontacting the electrode the smallest possible extension in thedirection of the electric field. This inhibits the movement of chargecarriers and prevents the formation of damaging gas bubbles at theelectrodes. The requirements for affording these characteristics existin the novel condensers to an almost ideal extent, because theelectrodes are always firmly adhered to two different paper strips-sothat the formation of gas bubbles between the electrodes and the paperstrips carrying them is reliably precluded.

It will also be evident that the exposed surfaces of the electrodeswhich are deposited on the respective paper strips will under allcircumstances bound one side of a gap which is filled with the liquidsaturation dielectric and whose width or depth is dependent upon theroughness of the paper strip surface, with the other side of the gapbeing delimited and bounded by a synthetic plastic strip, that is thestrip 18, 24, 30 or 31. Because of this the width of this gap isnarrower than a gap which would exist between two juxtaposed paper stripsurfaces, for the reasons discussed earlier.

The width of this gap can be still further reduced, and any depressionsor roughnesses in the surface of the paper strip be at least partlyfilled, if synthetic plastic material is used for the plastic stripswhich swells during saturation with the liquid dielectric and thus atleast in part fills these depressions. Such synthetic plastics may begiven the swelling characteristic by preliminary heat treatment which ineach case will depend upon the synthetic plastic material utilized. Forinstance if an electrical condenser accord ing to the present inventionutilizes synthetic plastic strip or strips of low-swellingpolycarbonate, it is advantageous to impregnate them (after the usualvacuum-drying process) with mineral oil at temperatures of between 90and 130C, and of course it is understood that dielectric other thanmineral oil can be utilized for this purpose in accordance with theteachings of the prior art. Subsequently, the thus impregnated condenseris maintained at the above temperature range for several hours before itis cooled off. On the other hand, if the condenser utilizes plasticstrips of for instance polypropylene, which has a higher swellingtendency, then the condenser may for instance be dried in vacuum attemperatures of 90-130C, and may subsequently be cooled down totemperatures of between 60 and 90C to be impregnated with a liquiddielectric whose temperature may be below the temperature of thecondenser itself. Only when the dielectric has entered into thecondenser winding or roll, will the condenser then be maintained at thetemperature of impregnation or at a higher temperature for some hoursbefore it is subjected to cooling or is permitted to cool.

It will be understood that each of the elements described above, or twoor more together may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in aself-healing electrical condenser, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit of the presentinvention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting features thatfrom the standpoint of prior art fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent isset forth in the appended claims:

1. A self-healing electrical condenser, comprising at least one firstelectrode; at least two second electrodes flanking said first electrode;first dielectric separating means between said first electrode and oneof said second electrodes, said first separating means comprising npaper strips and m synthetic plastic strips wherein n is a whole numberexcluding zero and one, and m is a whole number including zero and one,with n m; and second dielectric separating means between said firstelectrode and the other of said second electrodes, said secondseparating means comprising N plastic strips and M paper strips whereinN is a whole number including one, M is a whole number including zero,with N M, said electrodes each being applied to one side of two paperstrips and the latter having uncovered sides which face each other, andsaid first and second dielectric separating means being electricallyconnected in parallel with each other.

2. A condenser as defined in claim 1, wherein said electrodes aremetallic coatings.

3. A condenser as defined in claim 1, wherein said first dielectricseparating means comprises two overlying paper strips having sidesfacing away from each other, said electrodes being applied to saidsides, and an additional paper strip sandwiched between two paperstrips; and wherein said second dielectric separating means comprises aplastic strip sandwiched between said first and said other of saidsecond electrodes.

4. A condenser as defined in claim 1, wherein said first dielectricseparating means comprises two overlying paper strips having sidesfacing away from each other, said electrodes being applied to saidsides; and wherein said second dielectric separating means comprises aplastic strip sandwiched between said first and said other of saidsecond electrodes.

5. A condenser as defined in claim 1, wherein said first dielectricseparating means comprises two overlying paper strips having sidesfacing away from each other, said electrodes being applied to saidsides, and a plastic strip sandwiched between said paper strips; andwherein said second dielectric separating means comprises two overlyingplastic strips having sides facing away from each other and respectivelycontacting said first electrode and said other second electrode, and apaper strip sandwiched between said plastic strips.

6. A condenser as defined in claim 1, wherein said plastic strips are ofpolycarbonate.

7. A condenser as defined in claim 1, wherein said plastic strips are ofpolypropylene.

8. A condenser as defined in claim 1, wherein said plastic strips are ofpolysulfone.

1. A self-healing electrical condenser, comprising at least one firstelectrode; at least two second electrodes flanking said first electrode;first dielectric separating means between said first electrode and oneof said second electrodes, said first separating means comprising npaper strips and m synthetic plastic strips wherein n is a whole numberexcluding zero and one, and m is a whole number including zero and one,with n> m; and second dielectric separating means between said firstelectrode and the other of said second electrodes, said secondseparating means comprising N plastic strips and M paper strips whereinN is a whole number including one, M is a whole number including zero,with N>M, said electrodes each being applied to one side of two paperstrips and the latter having uncovered sides which face each other, andsaid first and second dielectric separating means being electricallyConnected in parallel with each other.
 2. A condenser as defined inclaim 1, wherein said electrodes are metallic coatings.
 3. A condenseras defined in claim 1, wherein said first dielectric separating meanscomprises two overlying paper strips having sides facing away from eachother, said electrodes being applied to said sides, and an additionalpaper strip sandwiched between said two paper strips; and wherein saidsecond dielectric separating means comprises a plastic strip sandwichedbetween said first and said other of said second electrodes.
 4. Acondenser as defined in claim 1, wherein said first dielectricseparating means comprises two overlying paper strips having sidesfacing away from each other, said electrodes being applied to saidsides; and wherein said second dielectric separating means comprises aplastic strip sandwiched between said first and said other of saidsecond electrodes.
 5. A condenser as defined in claim 1, wherein saidfirst dielectric separating means comprises two overlying paper stripshaving sides facing away from each other, said electrodes being appliedto said sides, and a plastic strip sandwiched between said paper strips;and wherein said second dielectric separating means comprises twooverlying plastic strips having sides facing away from each other andrespectively contacting said first electrode and said other secondelectrode, and a paper strip sandwiched between said plastic strips. 6.A condenser as defined in claim 1, wherein said plastic strips are ofpolycarbonate.
 7. A condenser as defined in claim 1, wherein saidplastic strips are of polypropylene.
 8. A condenser as defined in claim1, wherein said plastic strips are of polysulfone.